Oil Sand Ore
Oil sand ore is essentially comprised of a matrix of bitumen, solid mineral material and water.
The bitumen component of oil sand ore includes hydrocarbons which are typically quite viscous at normal in situ temperatures and which act as a binder for the other components of the oil sand. For example, bitumen has been defined by the United Nations Institute for Training and Research as a hydrocarbon with a viscosity greater than 104 mPa·s (at deposit temperature) and a density greater than 1000 kg/m3 at 15.6 degrees Celsius.
The solid mineral material component of oil sand ore typically consists of sand, rock, silt and clay. Solid mineral material may be present its oil sand ore as coarse solid mineral material or fine solid mineral material. The accepted division between coarse solid mineral material and fine solid mineral material is typically a particle size of about 44 microns. Solid mineral material having a particle size greater than about 44 microns is typically considered to be coarse solid mineral material, while solid mineral material having a particle size less than about 44 microns is typically considered to be fine solid mineral material. Sand and rock are generally present in oil sand ore as coarse solid mineral material, while silt and clay are generally present in oil sand ore as fine solid mineral material.
A typical deposit of oil sand ore may contain (by weight) about 10 percent bitumen, up to about 6 percent water, with the remainder being comprised of solid mineral material, which may include a relatively small amount of impurities such as humic matter and heavy minerals.
Processing of Oil Sand Ore
Water-based technologies are typically used to extract bitumen from oil sand ore originating from the Athabasca area in northeastern Alberta, Canada. A variety of water based technologies exist, including the Clark “hot water” process and a variety of other processes which may use hot water, warm water or cold water in association with a variety of different separation apparatus.
In a typical water based oil sand extraction process, the oil sand ore is first mixed with water to form an aqueous slurry. The slurry is then processed to release bitumen from within the oil sand ore matrix and prepare the bitumen for separation from the slurry, thereby providing a conditioned slurry. The conditioned slurry is then processed in one or more separation apparatus which promote the formation of a primary bitumen froth while rejecting coarse solid mineral material and much of the fine solid mineral material and water. The separation apparatus may also produce a middlings stream from which a secondary bitumen froth may be scavenged. This secondary bitumen froth may be added to the primary bitumen froth or may be kept separate from the primary bitumen froth.
A typical bitumen froth (comprising a primary bitumen froth and/or a secondary bitumen froth) may contain (by weight) about 60 percent bitumen, about 30 percent water and about 10 percent solid mineral material, wherein a large proportion of the solid mineral material is fine solid mineral material. The bitumen which is present in a typical bitumen froth is typically comprised of both non-asphaltenic material and asphaltenes.
Processing of Bitumen Froth
This bitumen froth is typically subjected to a froth treatment process in order to reduce its solid mineral material and wafer concentration by separating the bitumen froth into a bitumen product and froth treatment tailings.
In a typical froth treatment process, the bitumen froth is diluted with a froth treatment diluent to provide a density gradient between the hydrocarbon phase and the water phase and to lower the viscosity of the hydrocarbon phase. The diluted bitumen froth is then subjected to separation in one or more separation apparatus in order to produce the bitumen product and the froth treatment tailings. Exemplary separation apparatus include gravity settling vessels, inclined plate separators and centrifuges.
Some commercial froth treatment processes use naphthenic type diluents (defined as froth treatment diluents which consist of or contain a significant amount of one or more aromatic compounds). Examples of naphthenic type diluents include toluene (a light aromatic compound) and commercial naphtha, which may be comprised of both aromatic and non-aromatic compounds. Froth treatment processes which use naphthenic type diluents (i.e., naphthenic processes) typically result in a relatively high bitumen recovery (perhaps about 98 percent), but also typically result in a bitumen product which has a relatively high solid mineral material and water concentration (also described as “bottom sediment and water concentration” or “BS&W content”).
Other commercial froth treatment processes use paraffinic type diluents (defined as froth treatment diluents which consist of or contain, significant amounts of one or more relatively short-chained aliphatic compounds). Examples of paraffinic type diluents are C4 to C8 aliphatic compounds and natural gas condensate, which typically contains short-chained aliphatic compounds and may also contain small amounts of aromatic compounds. Froth treatment processes which use paraffinic type diluents (i.e., paraffinic processes) typically result in a relatively lower bitumen recovery (in comparison with naphthenic processes), and in a bitumen product which has a relatively lower basic sediment and water (BS&W) content (in comparison with naphthenic processes). Both the relatively lower bitumen recovery and the relatively lower BS&W content may be attributable to the phenomenon of asphaltene precipitation, which occurs in paraffinic processes when the concentration of the paraffinic type diluent exceeds a critical level. This asphaltene precipitation results in bitumen being lost to the froth treatment tailings, but also provides a cleaning effect in which the precipitating asphaltenes trap solid mineral material and water as they precipitate, thereby separating the solid mineral material and the water from the bitumen froth.
Froth treatment tailings therefore typically contain solid mineral material, water, froth treatment diluent, and small amounts of residual tailings bitumen (perhaps about 2 to 12 percent of the bitumen which was contained in the original bitumen froth).
Much of the froth treatment diluent is typically recovered from the froth treatment tailings in a tailings solvent recovery unit (TSRU). The froth treatment tailings (including the tailings bitumen) are then typically disposed of in a tailings pond.
Processing of Bitumen Froth Treatment Tailings to Recover Residual Bitumen
A significant amount of bitumen from the original oil sand ore is typically lost to the froth treatment tailings as tailings bitumen. There are both environmental incentives and economic incentives for recovering all or a portion of this tailings bitumen. The prior art includes attempts to recover bitumen from bitumen froth treatment tailings.
Canadian Patent No. 1,081,642 (Porteous) describes a method for treating froth treatment tailings obtained directly from a dilution centrifuging circuit which comprises introducing the tailings into a flotation cell, subjecting the tailings to agitation and flotation using gas introduced into the base of the body of tailings in order to recover bitumen and diluent as froth and in order to reject a portion of the solids and water as underflow, and removing the froth from further treatment.
Canadian Patent No. 1,094,484 (Lane et al.) describes a method similar to the method in Porteous, with the added steps of mixing the froth with a further portion of hydrocarbon diluent, treating the diluted froth in a scroll-type centrifugal separator to reject solids, water and a minor part of the hydrocarbons as tailings and produce a first product stream comprising hydrocarbons, water and a minor part of the solids, and treating the first product stream in a disc-type centrifugal separator to reject water, solids and a minor part of the hydrocarbons as tailings and produce a second product stream comprising hydrocarbons and a minor part of the water and solids.
Canadian Patent No. 1,238,597 (Seitzer) describes a process for the recovery of diluent and bitumen from the predominantly aqueous phase separated from an electrostatic treater used to separate bitumen from tar sands tailings to which a diluent such as naphtha has been added by adding a clay deflocculant to such diluted tailings, allowing separation to a top organic layer and a bottom aqueous layer essentially free of organic material, and separating the layers to recover the organic diluent and the bitumen.
Canadian Patent No. 1,252,409 (St. Amour et al.) describes a method for recovering bitumen from a waste sludge obtained from a retention pond used to store tailings from water extraction of bitumen from tar sands. The tailings comprising the waste sludge are collected from various processing steps of the “hot water” process for primary extraction of bitumen from tar sands. The method includes the steps of conditioning the sludge by removing carbon dioxide and methane and thereafter reducing the viscosity of the sludge, subjecting the conditioned sludge to air flotation in an induced air type of flotation cell in order to obtain a froth, subjecting the froth to a froth settler wherein the mineral tailings are drained off and delivered to a cleaner cell for further processing, diluting the froth from the froth settler with water, deaerating the diluted froth, and separating a bitumen product from the froth. Separating the bitumen product from the froth includes diluting the deaerated froth with hot naphtha and heating the froth, feeding the diluted and heated froth to a hydrocyclone, feeding the overflow from the hydrocyclone to a centrifuge, and recovering the overflow from the centrifuge as the bitumen product.
Canadian Patent No. 2,662,346 (Moran et al.) and corresponding U.S. Pat. No. 8,382,976 (Moran et al.) describe a method for recovering tailings bitumen from froth treatment tailings. The method includes separating a froth treatment tailings and a fine mineral material fraction, providing the fine mineral material fraction as a first feed material, conditioning the first feed material in order to produce a conditioned first feed material, providing a second feed material which is derived from the conditioned first feed material, and subjecting the second feed material to solvent extraction in order to produce an extract containing an amount of the tailings bitumen. The method may further include dewatering the conditioned first feed material in order to produce the second feed material, and clarifying the extract to produce a clarified extract containing an amount of the tailings bitumen.
Processing of Bitumen Froth to Recover Heavy Minerals
The prior art includes attempts to recover heavy minerals from bitumen froth.
Canadian Patent No. 861,580 (Bowman) describes a process for the recovery of heavy metals from a primary bitumen froth. The process includes introducing a fluid slurry of bituminous sand containing heavy metal into a body of water, whereby a froth containing bitumen and increased concentrations of heavy metal rises to the top of said body of water and sand settles to the bottom thereof, and recovering heavy metal from said froth.
Canadian Patent No. 879,996 (Bowman) describes a process for the recovery of heavy metals from a secondary bitumen froth. The process includes introducing a fluid slurry of bituminous sand containing heavy metal into a body of water whereby bituminous froth is floated to the top of such body of water and recovered therefrom while sand is allowed to settle to the bottom of such body of water for removal therefrom, withdrawing water containing fines and bitumen from an intermediate portion of such body of water and passing same to a second body of water wherein additional bituminous froth is floated to the top and recovered therefrom, and recovering heavy metal from such additional both.
Canadian Patent No. 927,983 (Fences) describes a process for the recovery of heavy metal materials from primary bitumen froth. The process includes introducing a fluid slurry of bituminous sand into a body of water whereby a froth containing bitumen and solids floats to the top of the water and is recovered therefrom. Solids are recovered from this froth and the recovered solids are treated with sodium hydroxide and then subjected to a flotation treatment using aeration gas. During the flotation treatment, solids other than heavy metal are selectively floated and heavy metals, especially zircon, remain in the bottom of the flotation zone from which they may be recovered.
Processing of Bitumen Froth Treatment Tailings to Recover Heavy Minerals
The solid mineral material which is included in the froth treatment tailings comprises an amount of heavy minerals. Heavy minerals are typically considered to be solid mineral material which has a specific gravity greater than that of quartz (i.e., a specific gravity greater than about 2.65). The heavy minerals in the solid mineral material which is contained in typical froth treatment tailings may include titanium metal minerals such as rutile (TiO2), anatase (TiO2), ilmenite (FeTiO3) and leucoxene (typically an alteration product of ilmenite) and zirconium metal minerals such as zircon (ZrSiO4). Titanium and zirconium bearing minerals are typically used as feedstocks for manufacturing engineered materials due to their inherent properties.
Although oil sand ore may contain a relatively low concentration of heavy minerals, it is known that these heavy minerals tend to concentrate in the bitumen froth which is extracted from the oil sand ore, and therefore become concentrated in the froth treatment tailings which result from froth treatment processes, primarily as coarse mineral material. As a result, froth treatment tailings may typically contain a sufficient concentration of heavy minerals to provide an environmental and economic incentive to recover these heavy minerals fern the froth treatment tailings. The prior art includes attempts to recover heavy minerals from bitumen froth treatment tailings.
Canadian Patent No. 1,013,696 (Baillie et al.) describes a process for producing from froth treatment tailings a quantity of heavy metal compounds such as titanium and zirconium minerals which are substantially free of bitumen and other hydrocarbon substances. The process includes separating bitumen froth together with solid components including heavy minerals from the sand in a main separation zone; separating the bitumen froth from the solid components, thereby forming a mineral waste product stream containing solid components including heavy minerals selected from the group consisting of titanium and zirconium and minerals, and combinations thereof; adding to the mineral waste product stream a liquid hydrocarbon solvent boiling in the range of 100 to 600 degrees Fahrenheit and containing at least 10 volume percentage aromatic hydrocarbons; separating the minerals from the solvent-mineral waste product mixture; and washing the minerals to remove the remaining solvent, thereby producing a quantity of heavy metal compounds substantially free of bitumen and other hydrocarbon substances.
Canadian Patent No. 1,076,504 (Kaminsky et al.) describes a process for concentrating and recovering titanium and zirconium containing minerals from froth treatment tailings. An oily mass of solids tailings containing a high concentration of heavy minerals, in the order of 10% by weight titanium and 4% zirconium, is derived from flotation of bitumen during hot water extraction of bituminous sands, and subsequent separation of most of the bitumen from associated solids. The tailings are introduced into a hot reaction zone and contacted with oxygen while agitating the solids. The bitumen associated with the solids is burned, as is residual coke left from the combustion of the bitumen. The product particles are discrete, dry and clean. They can be slurried with water and passed through gravity concentrating means, such as a spiral, to produce a concentrate containing in the order of 18% titanium and 8% zirconium.
Canadian Patent No. 1,088,883 (Trevoy et al.) describes a dry separatory process for concentrating titanium-based and zirconium-based minerals from first stage centrifuge froth treatment tailings. The titanium and zirconium-based minerals, present in the first stage centrifuge tailings from the hot water process for extraction of bitumen from bituminous sands, may be concentrated by a dry screening process. The tailings are burned off to provide a dry, essentially carbon-free, mineral mixture. By screening the mixture into three streams of different particle size range, silica and clays may be rejected as coarse and fine materials respectively, while titanium and zirconium minerals may be concentrated in the intermediate stream. The titanium and zirconium concentrate stream may be advanced to high tension and magnetic separation steps known in conventional processing of heavy minerals, for further beneficiation.
Canadian Patent No. 1,326,571 (Ityokumbul et al.) describes a process for recovering metals such as titanium and zirconium from froth treatment tailings. The process comprises ensuring that the pH of the a tailings slurry is in the range of from about 8 to about 11.5, subjecting the slurry to a flotation step in a flotation vessel comprising injecting air to cause flotation of a substantial amount of said metals in a froth above the siliceous and other unwanted material, and removing the floating froth containing the substantial amount of metals from the remainder of the slurry.
Canadian Patent No. 2,426,113 (Reeves et al.) describes a process for recovering heavy minerals from froth treatment tailings. The process includes contacting a tar sands-derived solids fraction with water at a temperature of at least about 100 degrees Fahrenheit to cause production a bituminous phase and a heavy minerals phase; and separating the heavy minerals phase from the bituminous phase.
Canadian Patent Application No. 2,548,006 (Erasmus et al.) and corresponding U.S. Patent Application Publication No. U.S. 2007/0272596 A1 (Erasmus et al.) describe a process for recovering heavy minerals from oil sand tailings (i.e., froth treatment tailings) in which the tailings are first “deslimed” in a designing means in order to remove a portion of the free fines and residual bitumen therefrom. The desliming means is comprised of one or more enhanced gravity separators, such as hydrocyclones or centrifuges. The deslimed oil sand tailings are then processed by being sequentially attritioned in an attritioner and separated in a separation means to separate the heavy minerals from other coarse solids present in the deslimed oil sand tailings and produce a concentrated heavy minerals fraction. The attritioner may be a Denver Cell™ type attritioner. The separation means may be comprised of a wide variety of separation apparatus and/or of combinations of such separation apparatus. The concentrated heavy minerals fraction may be further processed to remove residual bitumen therefrom and thereby produce a washed concentrated heavy minerals fraction. No processing is described for the slimes which are removed by the desliming means.
Canadian Patent No. 2,693,879 (Moran et al.) and corresponding U.S. Pat. No. 8,852,429 (Moran et al.) describe a method for processing froth treatment tailings. The method includes separating the froth treatment tailings in order to produce a coarse mineral material fraction and a fine mineral material fraction therefrom, subjecting the coarse mineral material fraction to froth flotation in order to produce a heavy mineral concentrate and a coarse mineral material tailings therefrom, and subjecting the heavy mineral concentrate to solvent extraction in order to produce a debitumenized heavy mineral concentrate and a bitumen extract therefrom.
In light of the large industrial scale of processes for oil sands ore processing, even incremental improvements in process parameters may have a substantial practical effect on the economics and environmental impacts of oil sands ore processing. Such environmental impacts may include demand on water resources, emissions of volatile organic compounds, emissions of greenhouse gases, and contamination of water supplies with bitumen, heavy minerals, and diluent. Therefore, notwithstanding the existence of methods to the prior art, there remains a need for methods for recovering bitumen, heavy minerals, and water from froth treatment tailings, and in particular from froth treatment tailings that are produced from paraffinic froth treatment processes and that comprise asphaltenes and non-asphaltenic material in the bitumen. Such methods are preferably are more effective in the recovery of bitumen, heavy minerals, and water, and more efficient in terms of the amount of diluent and make-up water consumed in the method.